DOE/RL-97-59
Revision 0

1.0 INTRODUCTION

1.1 BACKGROUND

On May 14, 1997, at 7:53 p.m., a chemical explosion occurred in Tank A-109 in Room 40 of the Plutonium Reclamation Facility (Facility) on the Hanford Site, north of Richland, Washington. The Facility, also known as Building 236-Z, is an inactive processing facility located at the Plutonium Finishing Plant (PFP). The explosion occurred when a highly concentrated solution of hydroxylamine nitrate (HN) and nitric acid (HNO₃) autocatalytically reacted inside Tank A-109.

On May 16, 1997, Lloyd L. Piper, Deputy Manager, acting for John D. Wagoner, Manager, U.S. Department of Energy (DOE), Richland Operations Office (RL), formally established an Accident Investigation Board (Board) to investigate the explosion in accordance with DOE Order 225.1, Accident Investigations.

1.2 FACILITY DESCRIPTION

The PFP (see Exhibit 1) is located in the 200 West Area of the DOE Hanford Site in the state of Washington. The Hanford Site is a 560-square-mile area with limited access. The 200 West Area is a 2,000-acre area near the center of the Hanford Site. The PFP is located within a fenced protected area. The principal PFP structure, Building 234-5Z, was completed in 1949 to convert plutonium-nitrate to plutonium metal and to fabricate plutonium metal parts.

Plutonium reclamation equipment is housed in the Facility, which was completed in 1964. It was designed as a multipurpose facility to process plutonium-bearing scrap to recover the plutonium. The Facility began full operation in 1964 and ceased operations in 1987, when it was placed on interim standby status pending restart. Because of mission changes, RL directed that the Facility be shut down in December 1993.

Exhibit 1. The Plutonium Finishing Plant and Plutonium Reclamation Facility.

The DOE Environmental Managements Office of Nuclear Material and Facility Stabilization (EM-60) has line responsibility within DOE Headquarters for the Facility. The DOE Richland Operations Office (RL) provides oversight of contractor operations at the Hanford Site. Since October 1, 1996, Fluor Daniel Hanford, Inc., under contract to RL, manages and integrates the scope of work defined in the Project Hanford Management Contract. The B&W Hanford Company manages and operates the Plutonium Finishing Plant, which includes the Plutonium Reclamation Facility (hereafter referred to as Facility), under subcontract to Fluor Daniel Hanford, Inc. The Westinghouse Hanford Company operated the Facility from June 1987 through September 1996, as the managing and operating contractor for the Hanford Site. During contractor change-over, the Facility line management staff remained intact.

1.2.1 PRF Description and Structural Specifications

The PRF is connected to Building 234-5Z by Building 242-Z (see Exhibit 1). The PRF is a four-story structure, with a two-story penthouse. The dimensions of the multi-level portion of the PRF are approximately 79 feet wide by 71 feet long, and 47.5 feet tall. The principal internal feature of the PRF is a single process equipment cell that is 32 feet wide by 52 feet long.

The PRF was designed in accordance with the 1961 Uniform Building Code (ICBO 1961). The PRF is a reinforced-concrete structure, except for the roof and the fourth-floor ceiling. The roof has open-web steel joist framing, steel decking, rigid insulation, and graveled built-up roofing.

1.2.2 Facility Fourth Floor and Room 40 Description

During plant operations, the fourth floor of the Facility (see Figure 1) was used for chemical preparation and miscellaneous treatment. The fourth floor houses Operating Control Room 44, Glovebox Room 43, Miscellaneous Treatment Room 41, and Column Room 42 in which vertical sections of two liquid-extraction columns (housed in a glovebox) penetrate the room from above and below. Chemical makeup vessels are located in Chemical Preparation Room 40 (see Exhibit 2). Room 40 contained nonradioactive chemicals.

Figure 1. Schematic of the Fourth Floor of the Plutonium Reclamation Facility.

NOTE: Details shown for Room 40 only.

Exhibit 2. Facility Room 40 Prior to May 14, 1997.

The Facility building ventilation system is designed for once-through flow to allow outside air to flow from uncontaminated areas to contaminated areas, then through a high-efficiency filter system before being exhausted by fans to the atmosphere via the PFPs main stack (Stack 291-Z-1).

During Facility operations, an alarmed monitor that was capable of detecting nitrogen oxide (NO) and nitrogen dioxide (NO₂) gases was in Room 40 to monitor the breathing air space. This monitor was part of the Facility worker protection system and was used to warn workers of elevated NO and NO₂ gas levels if the concentrated nitric acid that was contained in the Room 40 storage tanks decomposed and released those gases. On transition of the Facility from operations to shutdown, the nitric acid was removed from the storage tanks in Room 40 and the monitor was taken out of service. If the monitor had been in service before the explosion, it may have detected NO and NO₂ as it escaped from Tank A-109 into the Room 40 breathing air space, and may have set off an alarm. However, it is unknown whether sufficient quantities of NO and NO₂ would have existed in the room immediately before the autocatalytic reaction occurred to cause the monitor to alarm. However, if the monitor had been in service and had set off an alarm immediately before the autocatalytic reaction occurred, it may only have served to bring workers into the room to investigate, and to potentially result in serious, or fatal, injuries.

1.2.3 Tank A-109 Description

Tank A-109 (see Figure 2 [393K]) was a 400-gallon capacity chemical make-up tank and was set on a 6,000-pound capacity, industrial scale with a dial indicator marked in 10 pound increments. The volume of liquid in the tank is determined by reading the weight of solution from the dial and converting it to gallons of liquid. The tank is constructed of 347 stainless steel and measures 5 feet tall and 4 feet in diameter. Chemical make-up lines are connected to Tank A-109 for adding water, HN, hydrazine, and HNO₃. Tank A-109A, a 20-liter Pyrex^TM glass tank, was located above Tank A-109. Use of hydrazine was eliminated from the process in the mid-1980s and Tank A-109A was emptied and retained in place. Tank A-109 was equipped with a 1-inch overflow line that discharged to a basin below the tank, and a 1-inch vent line that connected to a forced air ventilation header. Tank A-109 was equipped with a motorized agitator that was attached to the outside of the tanks lid; an agitator shaft and mixing propellers were suspended from the tank lid to mix the solution inside the tank. The lid was attached to the tank with twenty-eight 5/8-inch stainless steel bolts made of 18-8 stainless steel. Tank A-109 has a 2-inch sloped bottom to ensure that the tank contents drain completely. Tank A-109 was not equipped with temperature indication capability.

The vent header links all of the chemical preparation tanks in Room 40 of the Facility to the E-3 exhaust duct, which vents to the Facility Buildings 291-Z exhaust and out the 291-Z-1 stack. No valving exists on either the overflow line, the vent line, or the vent header.

Figure 2. Schematic of Tank A-109.

1.3 SCOPE, CONDUCT AND METHODOLOGY OF THE INVESTIGATION

The scope of the Boards investigation was to review and analyze the circumstances of the events that led to the explosion; to analyze facts and to determine the causes of the accident; and to develop conclusions and judgments of need that may help prevent a recurrence of the accident. The scope also included the application of lessons learned from similar accidents within DOE. In addition to this detailed report, a Summary Report has also been prepared that provides a concise review of the facts and conclusions of this report, with an emphasis on management issues (DOE/RL-97-63).

Evaluation of emergency and occupational health response to, and radiological and chemical releases from, the explosion was not within the scope of this investigation, but has been analyzed by the RL Environment, Safety and Health organization (DOE/RL-97-62).

This report does not address the applicability of environmental regulations to the materials that were stored in Tank A-109. The Washington State Department of Ecology, the lead regulatory agency for such matters, is conducting an independent investigation to determine if state laws or regulations were violated. The Board has provided Washington State Department of Ecology representatives with full access to information that is available to the Board.

The Board conducted its investigation, focusing on the role that DOE and its contractor organizations and management systems may have had in the accident, by using the following methodology:

• Facts relevant to the accident were gathered through interviews, document reviews, and data collected at the Facility.

• Laboratory experiments and analyses were performed to determine the chemical, physical, and mechanical basis for and effects of the explosion.
• Barrier analysis (see Section 2.3), change analysis (see Section 2.4), and events and causal factors charting (see Section 2.5) were used to provide supportive correlation and identification of the accidents causes.
• Based on analysis of the data, judgments of need for corrective actions to prevent recurrence were developed.

Tier Diagraming was then used to hierarchically categorize the causal factors derived from the events and causal factor analyses, for determining the root and contributing causes.

Continue to Section 2